Study On Properties And Influencing Factors Of Pervious Concrete By Solid Waste Materials

Pervious concrete is a kind of green and ecological functional concrete,which can significantly improve the urban hydrological environment and reduce the urban sound pollution and light pollution.With the acceleration of urbanization in China,raw materials such as cement and natural gravel aggregates needed for concrete are in short supply.In this paper,solid waste materials are mainly used to prepare pervious concrete,with steel slag and recycled brick aggregate as aggregate,lithium slag powder as admixture,which can improve the comprehensive utilization rate of solid waste resources and reduce the production cost of pervious concrete,and it is of great significance for the promotion and application of pervious concrete.The effects of raw material properties and composition on the workability,mechanical properties,permeability and long-term durability of pervious concrete are systematically studied.The main research contents and corresponding conclusions of this article are as follows:The influence of water-cement ratio,silica fume content,admixture types and content on the rheological properties of cement paste were studied,and the appropriate range of slurry fluidity was put forward to be between 250 mm and 280 mm.Based on the analysis of the adhesion behavior and stress of cement paste on the surface of fresh pervious concrete aggregate,it is proved that the static yield stress of cement paste has a upper and lower critical value,and between the upper and lower critical values,the pervious concrete works well.Based on the original molding method,the "weight control method" was proposed to solve the problem of large dispersion of the strength data of pervious concrete by controlling the pervious concrete specimen at the same weight level.On this basis,the effects of water-cement ratio,silica fume and lithium slag powder content,aggregate types and particle size,and aggregate-cement ratio on mechanical properties of pervious concrete were studied.The results show that the strength of pervious concrete increases with the decrease of water-cement ratio,aggregate-cement ratio and aggregate particle size under the condition of consistent slurry fluidity.The types of aggregate have a greater influence on the strength of pervious concrete.The compressive strength of pervious concrete prepared with steel slag can reach up to 53.4MPa,while the compressive strength of pervious concrete prepared with recycled brick aggregate is about 10 MPa.In the first 28 days curing age,the use of lithium slag powder led to a decrease in the strength of pervious concrete;at the 90 days age,with the increase of lithium slag powder,the strength of pervious concrete increases first and then decreases,which reaches the peak at 25% lithium slag powder content,and the peak of compressive strength of pervious concrete prepared with steel slag is 39.6Mpa.Moreover,the mechanism of action of lithium slag powder in cement paste is proposed.According to Griffith’s fracture mechanics theory,the compressive strength model of pervious concrete is proposed.Using X-CT testing method and image analysis method to extract the connected pores of pervious concrete,the effects of water-cement ratio,lithium slag powder content,aggregate particle size and aggregate-cement ratio on the permeability of pervious concrete were studied.The results show that the influence of water-cement ratio and lithium slag powder content on the permeability coefficient of pervious concrete is not obvious under the condition of the consistency of slurry fluidity.With the increase of aggregate particle size and aggregate-cement ratio,the porosity and permeability coefficient increased significantly.On this basis,the relationship between the porosity of connected pores and permeability coefficient is obtained.Finally,using image analysis method studies the pore structure characteristics in the vertical direction of pervious concrete,and the relationship between the minimum porosity and the porosity of connected pores in the vertical direction of pervious concrete is obtained.According to the original rapid freeze-thaw method,a new experimental method for evaluating the freeze resistance of pervious concrete is proposed.The influence of lithium slag powder on the drying shrinkage and freeze resistance of pervious concrete were studied.The results show that the drying shrinkage of pervious concrete can be effectively reduced with the addition of lithium slag powder.As the increase of lithium slag powder,the drying shrinkage of pervious concrete decreases to a greater extent,which decreases by 27.2% with the content of 35%.Meanwhile,the use of lithium slag powder can improve the freeze resistance of pervious concrete.Within the range of15%-25%,the freeze resistance of pervious concrete is better.During the 125 th freezethaw cycle,the relative dynamic elastic modulus of pervious concrete with 25% lithium slag powder content is increased by 11.9%.